Automatic telephone system



G. E. SCHOMAKER.

AUTOMATIC TELEPHONE SYSTEM.

APPLlCATlON FILED MAY 23, 1917.

Patented Oct. 19, 1920.

um'ro srA'rs Parronies.

GEORGE E. SCHOMAKER, 01E CHICAGO, ILLINOIS, ASSIGNOR '10 AUTOMATICELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC TELEPHONE SYSTEM:

Specification of Letters Patent.

Patented Oct. 19, 1920.

Application filed May 23, 1917. Serial No. 170,337.

To all whom it may concern:

Be it known that I, Gnonon E. Sono- MAKER, a citizen of the UnitedStates of America, and a resident of Chicago, county of (look, and Stateof Illinois, have invented certain new and useful Improvements inAutomatic Telephone Systems, of which the following is a specification.

My invention relates in general to automatic telephone systems and moreparticularly to automatic systems of the type commonly known, astwo-wire, in which automatic switches at the exchange are controlledover the two sides of a calling subscribers line in series; and theprincipal object of the invention is the provision of new circuits forselector switches, with a view to rendering them immune from certaininherent defects which prior to my invention have been a source ofconsiderable trouble.

In s stems of the above general character the subscribers lines areusually provided with individual line switches, and upon the removal ofthe receiver at a calling subat the exchange is operated to extend theline circuit through to the first of the numerical trunking switches tobe used in establishing the connection. The selected numerical switch,commonly known as a first selector, is responsive to momentaryinterruptions of the line circuit subsequently produced by the operationof a calling device with which the substation is provided. In thepractical operation of such systems, it happens quite frequently that acalling subscriber, in removing his receiver to initiate the call, willaccidentally manipulate his switch hook so as to send a preliminaryimpulse over the line circuit immediately after the line switch hasoperated and before he has operated his calling device. In other words,if the receiver is carelessly removed, the first closure of the linecircuit may be followed by one or more interruptions before the receiveris completely disengaged from the hook. When this occurs, it follows asa matter of course that when the calling subscriber operates his callingdevice the first selector will already have been operated and that awrong number will therefore be obtained.

My invention cures the difficulty explained above by providing aselector circuit such that when a connection is ,extended to a selectorembodving my invention, a sequence of operations involving thedenergization of slow-acting relays takes place in the selector switchbefore the circuits for the operating magnets thereof are fullyprepared, thus introducing a time interval during which interruptions ofthe line circuit will be of no effect.

In addition to eliminating troubles due to the source above mentioned,my invention enables a selector switch wired in accordance therewith topass over open or defective trunks during the period of idle trunkselection, thus permitting the selector switch to automatically selectnot only an idle trunk, as is usual, but also a trunk the conductors ofwhich are electrically continuous, and even to a certain extent causingthe selector to reject trunks which terminate in selectors not inworking condition.

The precise manner in which the foregoing and other useful objects areattained may be readily understood from the following detailedspecification in which the operation of the circuits will be fullydescribed, reference being had to the accompanying drawing.

In the drawing, the figure shows my invention diagrammatically.

In the drawing the reference character A indicates a calling automaticsubstation whose line conductors 11 and 12 have been extended throughthe medium of the individual line switch C to the trunk line terminatingin the selector E. The selector E- has been operated to further extendthe connection to the trunk line comprising conductors 90, 91 and 92 andterminating in the second selector F, which in turn has been operated toestablish connection with the connector H. Of this latter switch, onlythe line and the release relays 150 and 151 are shown in the drawing.Inasmuch as the general construction and the trunking involved in anautomatic telephone system of this character is well known, only a briefgeneral description will be given, reference being had to prior patentshereinafter mentioned.

The substation A ma be of any approved type such, for examp e, as thesubstation shown in the British patent to Martin, No,

springs '7 an 1419 of 1910. As represented herein, it comprisesessentially t e receiver 2, transmitter 3, switch hook 4, ringer 5, andcondenser 6. Being an automatic substation there is also rovided a airof impulse wheel 9 through the medium of a hole dial (not shown); Theline conductors 11 and 12 of the substation A extend, to the exchangewhere they-terminate in the individual line switch 0 which is of theeneral type of line switch disclosed in the British patent to James, No.26,301 of 1906; bein however, of the particular type shown in S. LettersPatent, No. 1,078,690, "ranted Jan. 17, 1912, to Frank Newforth. Throu hthe medium of line switch C, the line of substation A, when calling, isgiven access to a plurality of trunk lines each terminating in a firstselector switch such as the selector E.

The line switch C and a plurality of similar line switches arecontrolled in their trunk selecting operations by means of a masterswitch WlllCh is shown in the drawing and indicated by the referencecharacter I). The master switch D is of the general type of masterswitch disclosed in the above mentioned British patent to James, No.26,301 of 1906; being, however, more nearly of the ty e disclosed in theBritish patent to Martin, 0. 1419 of 1910, also previously referred to.As is well known, the function of the master switch is to maintain thelungers of all the idle line switches which it controls in positionbefore the terminals of an idle trunk line.

The selector switch E, in which one of the trunk lines accessible tothe. line switch C terminates, is of the Jgeneral type of selectorswitch disclosed in I S. Letters Patent No. 815,321, granted March 13,1906, to Keith, Erickson, and Erickson; the side switch and privatemagnet being omitted, however, and the circuits being modified inaccordance with the two-wire system of control. The circuits are furthermodified in order to accomplish the objects of my invention, as will beexplained fully hereinafter.

The second selector F is similar to the first selector E except forslight circuit changes which will bepointed out in the description ofthe operation.

The connector H may be of any type which is adapted for operation in atwowire system of the character described. A connectorsuitable for thispur ose is shown in the atent to Newforth 0. 13901, reissued ril 13,1915.

While have shown throughout the drawing a plurality of batteries, it isto be understood that there is preferably but one battery having itspositive pole grounded, the

various battery leads shown in the drawing being connected together andextended to 8 control ed by imfpulse ingerthe live or ungrounded pole ofthe common characters have not been-applied to the different' batteriesand when in the specification a circuit is traced to battery it Wlll beunderstood that the circuit: extends to battery. I

Having given a general description of the apparatus mvolve' I will nowproceed to describe more in detail the operation of the same inestablishing the connection shown in' the drawing, particular attentionbeing paid to the features of the-operation with which my invention isconcerned. Inthe following, it will be assumed that the subscriber atthe substation A desires to call the subscriber at another substation inthe exchange'(not shown) which latter substation is accessible to theconnector H. When the calling subscriber at substation A removes hisreceiver to initiate the call, an energizing circuit is completed overthe line conductors 11 and 12 for the line relay 14 of the line switch Cin theusual well known manner. Upon attracting its armature, the

line relay closes a circuit for the pull-in winding 18. Upon energizing,the pull-in winding operates both the plunger arm 15 and the cut-offarmature 16; the former, through the medium of its plunger (not shown)forcing the bank springs 30 to 33, inclusive, into enga ement,respectively, with contacts 34 to z inclusive; and the latterdisconnecting the lines 11 and 12, respectively, from ground and fromthe line relay'14. By the engagement of the bank springs 30 and 33 withcontacts 34 and 37, respectively, the line conductors 11 and 12 areextended through normally closed contacts of the switching relay 57 tothe doublewound line relay of the selector E. The line relay 50 isaccordingly energized over the loop circuit including the substation Aand upon attracting its armature, closes a circuit for the slow-actingrelease relay 51. Upon ener izing, the release relay 51 closes a holdingcircuit for the line switch C which may be traced as follows: Ground atG working contact of armature 62 and the said armature, conductor 74,contact 70, sprin 71, conductor 73, contact 35, spring 31 and theholding winding 17 to battery. ince the line relay 14 is slow acting, itretains its armature to maintain the pull-in winding 18 energized untilafter the above holding circuit has been established. A branch of theholding circuit extends by way of conductor 20 to multiple test contactsin the banks of the connector switches having access to the line ofsubstation A where by a ground potential on the said contacts, the lineis made busy. By the engagement of bank sgg'ing 32 with contact 36 themaster" switch is operated in the usual manner to moreover wound with asmaller size wire, so

that it contains a much smaller number of turns; relay 53' therefore isnot energized upon the closure of the above circuit. Relay 57, however,is energized and attracts its armatures to the position shown in thedrawing, thereby breaking the circuit of the line relay 50. Upondeenergizing, relay 50 closes a circuit for the low resistanceslow-acting relay 52 as follows: ground at G armature 60 and its restingcontact, resistance 72, working contacts of armature 61, winding'ofrelay 52, and the winding of the vertical magnet 55 to battery. Owing tothe inclusion of the resistance 72 in the above circuit, the verticalmagnet 55 is not operated. Relay 52, however, energizes and at itsarmature 75 connects ground G to conductor 73 by Way of spring 71, atthe same time se arating the said spring from contact 70. y thisoperation ground G is substituted for ground G in therholding circuit ofthe line switch C. By attracting its armature 63, relay 52 prepares anenergizin circuit for relay 53 which will be described shortly. Aninstant after the relay 52 has energized, the slow-acting relay 51deenergizes, its circuit having been broken by the deenergization of theline relay 50. By the denergization of relay 51, round G is disconnectedfrom conductor 4 at armature 62 and at the same time the, circuit ofrelay 52 is brokenat armature 61. Thus it will be seen that since thepreviously described energizing circuit of relay 57 includes thegrounded conductor 74, the. circuits of this relay and the relay 52 willbe broken simultaneously. Owin to the fact that relay 52 is slow-acting,owever, relay 57 deenergizes first and again closes the circuit of theline relay 50.. Relays 50 and 51 now energize in rapid succession withthe result that ground G is again connected to conductor 74. The relay57 is not again energized, however, for since the slow-acting relay 52still retains its armatures, ground 2 is connectedto the junction ofrelays 53 and 57 by way of armature 63, thus short-circuiting relay ,5?and completing an energizing circuit for relay 53 which may be traced asfollows: ground at G working contactof armature 62 and the saidarmature, armature 63 and its working contact, armature 66 and Its rest-.ing contact, junction point 76, interrupter contact of the rotarymagnet 54, and the winding of rela 53 to battery. The u per terminalofre ay 57 being connecte to junction point 76 and its lower terminalbeing connected to conductor 74, this relay is 'short-circuited as abovementioned. Relay '53, upon energizing, prepares a circuit for the rotarymagnet .54 which will be described later, and at its armature 64completes a locking circuit for itself by connecting ground Gr tojunctionpoint 77 as follows: ground at G, working contact of 80 armature62 and the said armature, and armature 64 and its working contact tojunction point 77. This last described connection or looking circuit iseffective to maintain-relay v57 short-circuited and the.

relay 53 energized after the denergization of t e slow-acting relay 52which occurs an instant later.

"The foregoing operations, whereby the line switch C has been operatedto extend the line of the substation A to the selector E, resultingfinally in the continued energization of the relays 50, 51 .and 53 ofthe selector, have taken place automatically in response to the removalof the receiver at substation A. It will be seen that immediatelyfollowing the operation of the line switch C and the extension of theline conductors to the selector switch, a series of relay operationsoccur automatically at the selector, involving the energization anddeenergization of every relay in the switch except relay 53, whichlatter relay is not deenergized. These operations serve to prevent anypossibilityof closing the circuit of the vertical magnet 55 until aftera definite time has elapsed, dependin on the speed at which the relaysoperate. To explain this a little more fully, the vertical magnetcircuit, as is well known, is closed by-a momentary denergization of theline relay 50, relay 51 remaining energized, and extends as'follows:ground at G armature 60 and its resting contact,'resting contact ofarmature 69 and the said armature, armature 61 and its left-hand workingcontact, winding of relay 52, and the winding of-the vertical magnet55'to battery. This circuit is prepared at the first energization ofrelay 51, but relay 51 also closes the circuit of relay 57, and thislatter relay, upon' energizing, opens the circuit of the vertical magnetat its armature 69. The vertical magnet is thus prevented fromenergizing until relay 57 has deenergized and relays 50 and 51 haveagain become energized.v Looking at this feature of the operation fromanother angle, it will be seen that during the energization of relay 57the line conductorsare disconnected from the line relay 50 and areextended through to the line wipers 80 and 82. From this it follows thatthe selector switch is entirely free at this time of any control whichmay be exercised over the line conductors. The time interval introducedas above explained is not very long, being approximately one second orslightly over in duration; ut it has been found in practice to be ampleto obviate practically all wrong number troubles due to carelessness inthe subscribers when removing their receivers.

Having described in detail the extraordinary operations of the selectorE in accordance with my invention, I will now proceed to considerbriefly its usual operation in extending the connection to the calledline. When the subscriber at substation A operates his calling device inaccordance with the first digit of the called number, a series ofinterruptions is produced in the circuit of the line relay 50 in theusual manner.

At each interruption of its circuit, the line relay 50 deenergizesmomentarily and sends an impulse from ground Gr over the path previouslytraced through the relay 52 and the vertical magnet 55 to battery. Inresponse to these impulses, the vertical magnet operates to raise theswitch shaft step-bystep until the wipers 80, 81 and 82 arrive at thehorizontal level of bank contacts which constitute terminals of thetrunk lines extending to the desired main group of subscribers lines.The slow-acting relay 52 is energized in series with the vertical magnetand retains its armatures in operated position during the series ofimpulses. At the first upward movement of the shaft, the offnormalsprings 59 are closed to prepare a circuit for the rotary magnet 54which circuit is held open, however, during the vertical movement of-theswitch by the relay 52. At the end of the series of impulses, relay 52denergizes and closes the rotary magnet circuit which extends asfollows: ground at G working contact of armature 62 and the saidarmature, armature 63 and its resting contact, armature 65 and itsworkin contact, off-normal springs 59, and the winding of the rotarymagnet 54 to battery. Upon energizing, the rotary ma net operates torotate the wipers 80, 81 an 82 into engagement with the first set ofbank contacts in the level opposite which they were raised. Near the endof its stroke, the rotary magnet opens its interrupter contact, therebybreaking the energizing circuit of the relay 53. Upon denergizing, therelay 53 breaks the circuit of the rotary magnet which accordinglyretracts its armature and again closes its interrupter contact.Neglecting for the present any question of 0 en or defective trunklines, which will e referred to later, the operation now depends uponwhether the first trunk line, the terminals of which are now enga d bythe switch wipers, is busy or not. I this trunk line is busy, the testcontact with which the private wiper 81 is in engagementwill have groundpotential upon it, which ground potential will serve to maintain theswitching relay 57 short-circuited and also to again energize the relay53. The rotary magnet circuit is, therefore, again completed and thesame cycle of operation is repeated, whereby the switch wipers areadvanced into engagement with the next set of contacts. It will be seenthen, that the relay 53 will operate as an interrupter or stepping relayto advance the switch wipers through the medium of the rotary magnet aslong as the private wiper 81 continues to engage grounded or busy testcontacts. When a non-busy or ungrounded'test contact is reached, assumedto be the test contact 84, the relay 53 cannot again energize;

but the switching relay 57, being no longer short-circuited, instantlyenergizes in series with the said relay 53, which as before mentioned,is inoperative on this circuit. B

the attraction of its armature 69, the switching relay 57 opens thecircuit of the release magnet 56 to guard against the release of theswitch upon the de'energization of relays 50 and 51; shifts, at itsarmature 66, the private wiper 81 from connection with its upperterminal and into connection with its lower terminal and the conductor74; and at its armatures 67 and 68 disconnects the incoming lineconductors from the windings of the line relay 50 and extends theminstead by way of line wipers 80 and 82, bank contacts 83 and 85,conductors and- 92, and normally closed contacts of theswitching relay107 to the double-wound line relay 100 of the second selector F.

The line relay 100 is accordingly energized over the calling subscribersloop and completes the usual circuit for the slow-acting release relay101. Upon energizing, re-

holding winding 17 of the line switch (3' to battery. It is understoodthat the described holding circuit is completed before the slow-actingrelease relay 51 of the selector E has had time to denergize.

Owing to a sli ht difference in the circuits of selectors and E, theenergization of relays 100 and 101 as stated, are the only take relayoperations at the selector F which place when connection is extendedthereto. f 5

The calling subscriber may now 0 crate his calling device in accordancewith t e second digit of the desired number, thereby producing a seriesof interruptions in the circuit of the line relay. 100 of the selectorF. The line relay 100 is accordingly deenergized a number of times andat each deenergization, transmits an impulse from ground G through theslow-actin' relay 102 and the vertical magnet 105 to attery. In responseto these impulses, the vertical magnet operates to' raise the vswitchshaft step-by-step until the wipers 140,'-141,fand- 142 arrive at thehorizontal level of the bank contacts which constitute the 'termi nalsof trunk lines extending to the desired roup of connector switches. Theslow-actng relay 102 is energized in series with the vertical magnet andretains its armatures attracted during the series of impulses. Thus itwill be seen that during the vertical movement of the switch ground(iris replaced by ground G this operation is of no particularconsequence just at the present time. At the first upward movement ofthe shaft, the off-normal springs 159 are closed thereby completing aninitial energizing circuit for" relay 103 which may be traced asfollows: ground at. G", workmg contactof armature 110 and the saidarmature, armature 111 and its working contact,

armature 112 and its resting contact, interrupter contact of the rotarymagnet'104f.

off-normal springs 159 and the winding o relay 103 to battery. lllponenerglzlng, re-

lay 103 locks'itself to ground G at its upacting relay 102 denergizes atthe end of the series of impulses, it completes at the resting contactof its armature 111 the pre-" viously mentioned circuit of the rotarymagnet 104. Upon energizing, therotary magnet operates to rotate thewipers 140, 141, and 142 into engagement with the first set of bankcontacts in the level opposite which they were raised. In case the firsttrunk line is busy, the wipers are rotated in search of an idle trunkline under control of the private wiper 141 and the steppingrelay 103.Since this operation has een fully test contact of an idle trunk lineassumed to be the .test contact 163, the rotation of the switch willcease, and the. switching relay 107, heretofore *sho'rt-circuited eitherfrom ground Gr or from grounded bus test contacts, will energize withthe fol owing results: At its lower armature the circuit of the releasemagnet 106 is opened in the usual manner; at its upper armature theconnection of the private wiper 141 is shifted as described in the caseof selector E; and at its two inner armatures, the line conductors 90and 92 are disconnected from the windings of the line relay 100 and areex- 'tended instead by way of the line wipers 140 and 142'and conductors160 and 162 to the windings of the double-wound line relay '150 of theconnector H.

The line relay 150 is therefore energized over the calling subscribersline'and completes an energizin circuit for the slowacting relay 151.his latter relay, upon energizing, completes'a holdin circuit for theselector F and the other swltches which extend as'follows: ground at G,working contact of armature 115 and the said armature, conductor 161,bank contact 163, pri-' vate wiper 141, and'armature 112 and its workingcontact to junction point 116; where the circuit divides, one branchextending by way of the winding of relay 107 and the windlng of relay103 to battery, and the other branch extending by way of i normallyclosed contacts of relay 102 to the conductor 91' where it joins thepreviously tracedholding circuit extending back to the selector vE andthe line switch 0.

The connector H is now operated in response to-the callin of theremainin digits in the desired num er to complete t e connection to thecalled subscribers line. These operations. are well known having beendescribed in the previously mentioned patents and will not be consideredin detail. It will be enough to say that when the connection iscompleted the called subscriber is signaled in the usual manner, andwhen he responds, conversation may :be held over the connection whichhas been established. The calling subscriber is supplied with talkingcurrent over the heavy line conductors and through the windings of therelay 150 of the connector switch. When the receiver is replaced at thesubstation A at the end of the conversation, the relays 150 and 151 ofthe connector H are deenergizedand ground G is removed from theholdirfig circuit extending back to the selectors to the individual lineswitch (I. The switching relays 107 and 57 .of these selector switchesare accordingly deenergized whereupon the selectors are restored tonormal in and E and the usual manner through the medium of theirrespective release magnets 106 and 56. Upon the dei nergization of theholding windin 17 the plunger of the line switch C is withdrawn from thebank, whereupon all the apparatus involved in the connection will havebeen restored to ,normal.

The operation of the selector E will now be further considered for thepurpose of explainingits operation in passing over or rejecting opentrunks. From the description which has already been given, it Wlll beunderstood that after the selector switch has cut in or, in other words,after its switching relay 57 has operated to extend the connection tothe second selector F, the continued energization of the switching relayis dependent upon a holding circuit being established over the thirdconductor 91 by the relay 101 of the second selector. The failure toclose this holding circuit, which were it not for my invention wouldresult in the release of the selector switch and line switch, may be dueto a number of causes. For example, either of the conductors 90, 91 or92 may beactually open, the bank contacts in which these conductorsterminate in the selector E may be dirty, resulting in a poor wipercontact, or there may be one or more dirty relay contacts in theselector F. At any rate, prior to my invention, whenever a selectorswitch in a well known twowire system was operated, if ground was notimmediately fed back from the selector switch ahead, the operated switchwould immediately release. This is an undesirable result, for it makesit necessary for the calling subscriber to call his number over again.By my invention, when a selector switch, as the selector E for example,stops on an idle but open trunk line, it does not release but therotation is started again and continues until the next idle trunk lineis reached. If this second selected trunk line should also happen to beopen for any reason, the selector switch selects still another idletrunk line, continuing the operation until a trunk is selected which isin working condition.

For the purpose of explaining this feature, it will be assumed that thetrunk line comprising conductors 90, 91 and 92 was open at some pointwhen the selector E was operated to establish connection therewith, andthe operation of the selector under these circumstances will beexplained. When the wipers of the selector are brought to rest inengagements with the bank contacts 83, 84, and 85 and the switchingrelay 57 is energized, the line conductors incoming tothe selector E aredisconnected from the line relay 50 as previously explained and areextended through to the conductors 90. and 92. The relay 50, upondeenergizing,

closes an energizing circuit for the relay 52 which extends by way ofresistance 72, the winding of the said relay 52, and the winding of ,thevertical magnet 55 to battery. l)on energizing, relay 52 connects ground.1 to conductor-'73 as a substitute for ground G which is momentarilydisconnected an instant later, and also repares a circuit for thestepping relay 53., elay 51 now deenergizes and breaks the circuit ofrelay 57. By the de'energization of relay 57,

the circuit of the line relay 50 is reestablished, whereupon the relays50 and 51 immediately energize again. The slow-acting relay 52 stillbeing in operated position, the energization of relay 51 now results inthe short-circuiting of relay 57 and the closure of the circuit of thesteppin rela Upon energizing, relay 53 locks itse findependent of theslow-acting relay 52 and also prepares the rotary magnet circuit, whichis completed an instantlater when the relay 52 denergizes. Theseoperations are the same as those which took place when the connectionwas first extended to the selector switch, except for the fact that now,since the off-normal springs 59 are closed, the rotary magnet isoperated and the wipers of the selector are advanced into engagementwith the contacts associated with the next trunk line. Idle trunkselection now takes place as before and if it should happen for anyreason that the trunk next selected was open also, the wipers would beagain rotated, the trunk selecting operations being brought to a haltonly when an idle and working trunk is reached.

The operation of the second selector F in passing over open trunks ispracticall identical with the operation of selector under similarconditions. The selector F is wired slightly different from selector E,however, in order to prevent the preliminary operation of the relayswhen the selector is first connected with; for since in the case of thesecond selector, there is no occasion for removing the selector from thecontrol of the calling line, such relay 0 erations would serve no usefulpurpose. he off-normal springs 159 therefore are placed in the circuitof the stepping relay 103 rather than in the circuit of the magnet 104.Also it will be noticed that there is no resistance in the selector Fcorresponding to the resistance 72 in the selector E. This resistancemay be included if desired, but its omission causes no harm. Its purposeis solely to prevent the operation of the vertical magnet during thepreliminary relay operations at the selector immediately following theseizure thereof, and since the circuits which cause the reliminary relayoperations in the selector are not present in the selector F, noresistance is needed. It

is understood, of course, that the energization of the vertical magnetafter the switch has cut in is of no effect.

Having described my invention what I consider to be new and desire'tohave protected by Letters Patent will be pointed outin the appendedclaims.

What I claim as my inventionis:

l. In a telephone system, a selector switch having an operating magnetand a line 'relay, subscriber controlled means for energizing said relayand for subsequently deenergizing the same to close a circuit for saidmagnet, and means in said switch serving automatically to cause amomentary deenergization of said relay while preventing the energizationof said magnet.

2. In a telephone system, subscribers lines, an automatic selectorswitch having an operating magnet and controlling relays, means forextending a calling line to said switch, and circuits servingautomaticallyto energize every relay in said switch at least once whenconnection is extended thereto and for preventing at the same time theenergization of said magnet.

3. In a telephone system, subscribers lines, an automatic switch havingan operating magnet and a relay,means for extending a connection from acalling line and for controlling said relay, to operate said mag net,and automatic means for reducing the current flow in said 'magnettoprevent its operation for-a definite interval relay has been energized.

.4. In a telephone system, anautomatic switch, a line relay and anoperating magnet therefor, means for'seizing said switch and energizingsaid line relay, means for intermittently deenergizing said line relayto close the circuit of said magnet to operate said switch, andautomatic means for preventing the first closure of the circuit of saidmagnet from operating the switch.

5. In a telephone system, an automatic switch, a line relay and anoperating mag:

' net therefor, means for seizing said switch and for controlling saidline relay to ,close a circuit for said operating magnet to in after thecircuit is inefiective to operate said magnet.

6. In a telephone system, calling lines, an automatic switch, means forextending a connection from a calling line to said auto- I matic switchin response to the first closure of a line circuit, a line relay andoperating magnet for said switch, said line relay controlled bysubsequent interruptions of said line circuit to close a circuit forsaid operating magnet to operate said switch, and automatic means forrendering said line relay nonresponsive to any interruptions of the linecircuit which may occur for a certain time interval after the firstclosure of the line circuit.

7. In a telephone system, calling lines, an automatic switch, means forextending a connection from one of said lines to said automatic switchin response to the first closure of the line circuit of said line, a

circuit is closed by the line relay to prevent.

the operation of the switch.

8. In a telephone system, calling lines, an automatic switch, a linerelay" and an operating magnet for said switch, means for extending aconnection from one of said lines to said automatic switch to energizesaid line relay, a calling device on said line for controlling saidrelay to control the operation of the switch through the medium of saidmagnet, and automatic means for momentarily opening the circuit of saidline relay as soon as the switch is seized and forrendering said magnetinoperative momentarily to prevent a false operation of the switch.. vSigned by me at Chicago, Cook county,

Illinois, this 21st day of. Ma 1917.

GEORGE E. SCfilOM-AKER.

automatic means

